Question

Rozwiąż układ równań metodą podstawiania i sprawdź, czy znaleziona para liczb spełnia układ.

\left \{ {{7x+8y=9} \atop {5x+6y=7}} \right

Answer 1

7x+8y=9

5x+6y=7

 

7x = 9 - 8y

5x + 6y = 7

 

x = (9-8y)/7

5( 9-8y)/7 + 6y  = 7     /* 7

 

x = (9-8y)/7

5(9-8y) + 42y = 49

 

x = (9-8y)/7

45 - 40y + 42y = 49

 

x = (9-8y)/7

2y = 49 -45

 

x = (9-8y)/7

2y = 4     /:2

 

y = 2

x = ( 9 - 8*2)/7

 

y = 2

x = -7/7

 

y = 2

x= -1

 

spr.

7x+8y = 9

 7* (-1) + 8 * 2 = 9

-7 + 16 = 9

9 = 9

L=P

 

Answer 2

7x+8y=9

5x+6y=7

 

7x=9-8y   /:7

5x+6y=7

 

x=9/7-8/7y

5*(9/7-8/7y)+6y=7

 

x=9/7-8/7y

45/7-40/7y+6y=7

 

x=9/7-8/7y

-40/7y+6y=7-45/7

 

x=9/7-8/7y

-82/7y=4/7    /:(-82/7)

 

x=9/7-8/7*4/82

y=-4/82≈0,04

 

x≈1,23

y≈0,04